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st: allow debug output to be enabled or disabled via sysfs

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Change st driver to allow enabling or disabling debug output
via sysfs file /sys/bus/scsi/drivers/st/debug_flag.

Previously the only way to enable debug output was:

1. loading the driver with the module parameter debug_flag=1
2. an ioctl call (this method was also the only way to dynamically
disable debug output).

To use the ioctl you need a second tape drive (if you are
actively testing the first tape drive) since a second process
cannot open the first tape drive if it is in use.

The this change is only functional if the value of the macro
DEBUG in st.c is a non-zero value (which it is by default).

Signed-off-by: Shane Seymour <shane.seymour@hpe.com>
Reviewed-by: Laurence Oberman <oberman.l@gmail.com>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Odin.com>
This commit is contained in:
Seymour, Shane M 2015-10-12 04:31:17 +00:00 committed by James Bottomley
parent c59ab4e5af
commit d9b43a10f0
3 changed files with 45 additions and 1 deletions
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12
Documentation/ABI/testing/sysfs-driver-st Normal file
View file

@ -0,0 +1,12 @@
What: /sys/bus/scsi/drivers/st/debug_flag
Date: October 2015
Kernel Version: ?.?
Contact: shane.seymour@hpe.com
Description:
This file allows you to turn debug output from the st driver
off if you write a '0' to the file or on if you write a '1'.
Note that debug output requires that the module be compiled
with the #define DEBUG set to a non-zero value (this is the
default). If DEBUG is set to 0 then this file will not
appear in sysfs as its presence is conditional upon debug
output support being compiled into the module.

4
Documentation/scsi/st.txt
View file

@ -569,7 +569,9 @@ Debugging code is now compiled in by default but debugging is turned off
with the kernel module parameter debug_flag defaulting to 0. Debugging
can still be switched on and off with an ioctl. To enable debug at
module load time add debug_flag=1 to the module load options, the
debugging output is not voluminous.
debugging output is not voluminous. Debugging can also be enabled
and disabled by writing a '0' (disable) or '1' (enable) to the sysfs
file /sys/bus/scsi/drivers/st/debug_flag.
If the tape seems to hang, I would be very interested to hear where
the driver is waiting. With the command 'ps -l' you can see the state

30
drivers/scsi/st.c
View file

@ -4452,11 +4452,41 @@ static ssize_t version_show(struct device_driver *ddd, char *buf)
}
static DRIVER_ATTR_RO(version);
#if DEBUG
static ssize_t debug_flag_store(struct device_driver *ddp,
const char *buf, size_t count)
{
/* We only care what the first byte of the data is the rest is unused.
* if it's a '1' we turn on debug and if it's a '0' we disable it. All
* other values have -EINVAL returned if they are passed in.
*/
if (count > 0) {
if (buf[0] == '0') {
debugging = NO_DEBUG;
return count;
} else if (buf[0] == '1') {
debugging = 1;
return count;
}
}
return -EINVAL;
}
static ssize_t debug_flag_show(struct device_driver *ddp, char *buf)
{
return scnprintf(buf, PAGE_SIZE, "%d\n", debugging);
}
static DRIVER_ATTR_RW(debug_flag);
#endif
static struct attribute *st_drv_attrs[] = {
&driver_attr_try_direct_io.attr,
&driver_attr_fixed_buffer_size.attr,
&driver_attr_max_sg_segs.attr,
&driver_attr_version.attr,
#if DEBUG
&driver_attr_debug_flag.attr,
#endif
NULL,
};
ATTRIBUTE_GROUPS(st_drv);